A device of this type for controlling a gearbox is known from DE 199 31 973 A1. The known control device includes a pressure medium source, which is connected to a pressure limiting valve via a supply line. A first controllable valve device is connected to the pressure limiting valve, and is followed again by an actuating device to adjust the gearbox. The first controllable valve device includes two 3/2-way valves, which on one side are connected to the pressure limiting valve and on the other to the actuating device to adjust the gearbox. The pressure limiting valve as well as the first controllable valve device is actuated as a function of the pressure in the lines between the pressure-limiting valve on the one side and the 3/2-way valves on the other. In order to ascertain this pressure, the indicated document suggests arranging a pressure sensor inside the pressure medium line extending from the pressure-limiting valve to the first controllable valve device. Further, a second controllable valve device is provided, which serves to control a further actuating device. The second controllable valve device is connected directly to the pressure medium source, whereby this is again via the above-mentioned supply line. A further pressure sensor is provided in the supply line and serves to monitor the supply pressure. The pump allocated to the pressure medium source is actuated on the basis of the supply pressure ascertained, so that a constant supply pressure is assured inside the supply lines.